1. Field of Invention
The present invention relates generally to fluid directional control valves and more specifically to such valves which are electromagnetically operated.
2. Description of the Prior Art
In many fields of application of fluid power such as the field of automotive automatic transmission design, the use of directional control valves has been limited to those which employ cylindrical spools, spring biased and pressure activated. Such valves are generally close fit and therefore suffer greatly from their attendant intolerance of contamination which results in sticking. Recognition of this potential for unreliability can, in certain circumstances, dictate uneconomical redundancy in design. Furthermore, the spool-type valve does not lend itself well to use with electronic operators which are coming into increasing commercial use. Because of their contamination intolerance, direct actuation of such valves, as with solenoids, requires high force and massive structure, and pilot operation through a smaller intermediary valve increases cost and complexity.
It is well known in the art that ball-type valves are relatively contaminant tolerant, but their use in solenoid actuated applications has been primarily limited to relatively low force pilot valve applications rather than applications in which relatively large primary flow passes through the valve. The prior art devices also have shown the use of relatively large solenoids which conventionally operate against relatively high preload forces. They have also made use of close fit cylindrical parts moving in pressure fluid for ball actuation which detracts from the contaminant tolerance of the overall assembly. They have further permitted high contact stresses between the ball member and its associated actuator, which further detracts from reliability of the valve assembly. In addition, the prior art valves have been unduly complex and uneconomical to produce.